How the UK labour party can winWatch
The old left understood this well, Marx himself wrote against the mass importation of cheap foreign labour, so I find it baffling that so many in the Labour party today, even on the economic hard left are actually in favour of unfettered, open borders, when it is so highly detrimental to their core working class base. Their support for immigration seems to be solely ideological, it's as if keeping up the mere appearance of not being xenophobic or 'racist' is more important to them than not actively screwing over your own poor and working class populace.
But behind him stand what are essentially self-serving public school educated people who have no interested in running a country of society for everyone. They are simply in favour of ensuring they have it good. Everyone else? Well, there is no such thing as society is there?
On (1), if the Liberal Democrats ever were to join a "Progressive Alliance", their vote share would collapse. People seem to forget that the Lib Dems attract many right-wing voters who see them as safer opposition than Labour due to their economic outlook. The only gains they made in 2019 were in former Conservative seats, representing 'Remain' constituencies. If they were seen to be fighting for a Labour cause, they would lose a lot of support.
I think so long as the Tories have a majority or appear to these sorts won't mind too much - as we can see in the Amersham by election.
Why would the SNP or Plaid be interested in a pact then?
Mainly the SNP as that's where 50 seats live. Unless Labour were to offer support for a section 30 on an independence vote surely they'd not entertain it.
I think this is at the heart of the problem. If Labour really has to go cap-in-hand to an assortment of weirdos and is clearly in danger of compromising on what should be some of its most important policies (the integrity of the United Kingdom, ffs) then what is your middle-ground voter going to make of that? They're going to run a mile. Because there's (presumably) a reason people vote Labour rather than the Greens, Plaid, SNP or whatever.